The use of dispersio´n-free solvent extraction, through
microporous hydrophobic membrane has been investigated.
The hollow fiber contactor, with surface area of 1.4 m2 was used
to extract Cr(VI) (0.005-0.12 g/L) from aqueous sulphuric
acidic media (pH 2.5-4.2 ( 0.05). Several parameters such as
extractant concentration, feed acidity and metal concentration
in the initial aqueous solution were investigated. Results revealed
that 15% v/v Cyanex 923 in Exxsol D-100 as organic phase
and feed in the 2.5 pH range, gave optimum extraction (exceeding
95%) of Cr(VI) and it was possible to strip using 10 g/L
hydrazine sulfate (also with recoveries exceeding 95%). In this
step, Cr(VI) is immediately reduced to the less hazardous
Cr(III) state. Results also showed that under the various
experimental conditions, chromium(VI) extraction was ratecontrolled
by the interfacial reaction on the membrane surface.
Typical overall mass transfer coefficients values are 4.2 ×
10-5 and 3.6×10-6 cm/s for extraction and stripping operations,
respectively.